Radio communication system

Abstract

The present invention is directed to a wireless communication system capable of keeping a level of a wireless signal received by a relay apparatus (20) within a predetermined dynamic range. In a control apparatus (10), a transmitting section (102) converts a downstream electric signal into a downstream optical signal and transmits the downstream optical signal to the relay apparatus (20) via an optical transmission path (40). The relay apparatus (20) converts the received downstream optical signal into a downstream electric signal and transmits the downstream electric signal as a wireless signal to a wireless communication terminal (30) from a transmitting / receiving antenna section (204). In the relay apparatus (20), a level adjustment section (207) adjusts the level of the wireless signal transmitted by the relay apparatus (20) such that the receiving level of the wireless signal received by the relay apparatus is kept within a predetermined range.

Description

TECHNICAL FIELD [0001] The present invention relates to a system in which a control apparatus communicates with a wireless communication terminal via a relay apparatus, and more particularly to a system in which the control apparatus and the relay apparatus are connected to each other via an optical transmission path. BACKGROUND ART [0002] Recently, wireless communication systems in which a relay station for communicating with a wireless communication terminal wirelessly is connected to a control apparatus via an optical transmission path have been used (for example, Japanese Laid-Open Patent Publication No. 9-233050). [0003]FIG. 43 is a diagram showing a structure of a conventional wireless communication system described in Japanese Laid-Open Publication No. 9-233050. In the wireless communication system shown in FIG. 43, a control apparatus 19 converts a modulated signal into an optical signal and transmits the optical signal to the relay apparatus 29 via an optical transmission p...

AI Technical Summary

Benefits of technology

[0033] Accordingly, an objective of the present invention is to provide a wireless communication system capable of keeping the levels of wireless signals received by a relay apparatus within a predetermined dynamic range.

[0034] Another objective of the present invention is to provide a wireless communication system capable of fulfilling first through third requirements, i.e., keeping the levels of wireless signals received by a relay apparatus within a predetermined dynamic range, capable of keeping the leakage ratio of a wireless signal to a certain level or lower, and capable of keeping the D / U ratio of a wireless signal received by the relay apparatus at a certain level or higher.

Problems solved by technology

In the case where the level of a wireless signal received by the relay apparatus is too high, when the wireless signal is converted into an optical signal, the optical signal is distorted.

By contrast, in the case where the level of a wireless signal received by the relay apparatus is too low, the wireless signal to be received and noise cannot be separated from each other.

Out-band frequency components have adverse effects on other communication devices which communicate using the same frequency band as that of the out-band frequency components, electric devices existing in the vicinity of the wireless communication terminal, and the like.

The reason is that when the D / U ratio is too low, the relay apparatus cannot separate the signal to be received and noise from each other.

This complicates the structure of the system.

Even in the case where a signal is transmitted to a control apparatus using a frequency-division multiplexing system also, there is a problem that the structure of the system is complicated.

This complicates the structure of the relay apparatus and makes it difficult to reduce the size of the relay apparatus.

As a result, there is a problem that the system having such a structure is expensive.

As described above, the conventional wireless communication system described in the specification of Japanese Patent No. 2885143, although being capable of fulfilling the first requirement, has a problem of complicating the structure thereof.

Moreover, the IEEE802.11a Standard does not provide any regulation for the case where the relay apparatus uses wireless signals of a plurality of channels.

As described above, in the case where a plurality of communication terminals perform communication using two adjacent channels, normal communication may not be possible due to jamming from a signal of another channel, even if the wireless signal received by the relay apparatus has the quality in conformity to the Standard and the level of the wireless signal is within the dynamic range regulated by the Standard.

In such a case, the first and second problems can be solved, but the third problem of fulfilling the predetermined D / U ratio cannot be solved.

As described above, in the case where a plurality of communication terminals perform communication using two channels which are away from each other by a two-channel distance, normal communication may not be possible due to jamming from a signal of another channel, even if the wireless signal received by the relay apparatus has the quality in conformity to the Standard and the level of the wireless signal is within the dynamic range regulated by the Standard.

In such a case, the first and second problems can be solved, but the third problem of fulfilling the predetermined D / U ratio cannot be solved.

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